Highlights:

Step 1: Measure the Cushion and Cut the Fabric

Measure width and depth of cushion; add 1 inch to each measurement. Cut one piece of fabric to these measurements for cushion bottom. Measure height of cushion; double this amount and add 1 inch. Add this measurement to both the width and depth measurements and cut one piece of fabric to these measurements for cushion top and sides (for example, for a 22x20x4-inch cushion, cut the fabric 22 plus 8 plus 1 = 31 inches wide and 20 plus 8 plus 1 = 29 inches long).

Step 2: Trace the Cushion

Center cushion on wrong side of second fabric piece; draw outline around cushion. Remove cushion.

Step 3: Make Darts

Fold one corner of marked fabric in half diagonally to form mitered corner with right sides of folded corner facing. Sew a line perpendicular to the raw fabric edges, starting at the marked line and stopping 1/2 inch from the edge, forming a dart. Make a dart at all other corner in same manner.

Step 4: Trim the Fabric

Trim fabric at corners within seam to 1/2 inch; press seams open.

Step 5: Attach a Zipper

For zipper, with right sides facing and raw edges even, pin just the back edge of this piece to the cushion bottom with right side facing and raw edges matching. Mark zipper placement in center of pinned area; sew from corner to corner with 1/2-inch seam, using basting stitches in zipper area. Press seam open. Center and pin front of zipper to pressed open seam between marks. Baste 1/4 inch from seam on each side. With right side up, sew over basting lines to attach zipper. Remove hand and machine basting; open zipper several inches.

Step 6: Pin and Sew the Sides

Pin remaining three sides of bottom to the other three sides of the darted top and stitch with 1/2-inch seams, pivoting stitching at corners.

Step 7: Insert the Cushion

Turn right side out; press. Insert cushion through zipper opening. Zip to close.